Determination of ventricular pacing capture thresholds is important in order to ensure that a patient is receiving a desired pacing therapy or for configuring the resulting mechanical ventricular contraction to one or more sequentially delivered pacing of various amplitudes and sequences. During the delivery of sub-threshold capture pulses or refractory period pulses to augment mechanical contraction, it is important to establish that such sub-threshold or refractory pulses do not by themselves result in a separate mechanical ventricular contraction, but results instead in the mechanical augmentation of the contraction initiated by the capturing pacing pulse. At least one based accelerometer is used to determine the relevant pacing parameters including the upper threshold, shortest interval(s), waveform, or timing relative to another cardiac event, in order that the clinician is able to set a range of electrical pulses that does not cause separate mechanical ventricular contractions with each electrical stimulus. Additionally, a range of parameters can be determined in order to optimally augment each ventricular contraction using the minimal amount of energy. The configuration of the electrical pulses may therefore be within a specified range as required to minimize the device energy required while ensuring that the desired therapy is maintained. In either case an algorithm can be incorporated in the device and/or programmer to use a motion sensor to measure the mechanical effects of one or more ventricular pacing pulses from either the left or right ventricular chamber in order to optimize the net mechanical ventricular effect by determining the range of parameters for electrical stimulation that results in a within a range of non-capturing electrical pacing pulse(s).
During normal cardiac function, the atria and ventricles observe consistent time-dependent relationships during the systolic (contractile) phase and the diastolic (relaxation) phase of the cardiac cycle. During cardiac dysfunction associated with pathological conditions or following cardiac-related surgical procedures, these time-dependent mechanical relationships are often altered. This alteration, when combined with the effects of weakened cardiac muscles, reduces the ability of the ventricle to generate contractile strength resulting in hemodynamic insufficiency.
Ventricular dyssynchrony following coronary artery bypass graft (CABG) surgery is a problem encountered relatively often, requiring post-operative temporary pacing. Atrio-biventricular pacing has been found to improve post-operative hemodynamics following such procedures.
Cardiac pacing may be applied to one or both ventricles or multiple heart chambers, including one or both atria, to improve cardiac chamber coordination, which in turn is thought to improve cardiac output and pumping efficiency. Clinical follow-up of patients pacing therapy has shown improvements in hemodynamic measures of cardiac function, ventricular volumes, and wall motion.
Implantable sensors for monitoring heart wall motion have been described or implemented for use in relation to the right ventricle. A sensor implanted in the heart mass for monitoring heart function by monitoring the momentum or velocity of the heart mass is generally disclosed in U.S. Pat. No. 5,454,838 issued to Vallana et al. A catheter for insertion into the ventricle for monitoring cardiac contractility having an acceleration transducer at or proximate the catheter tip is generally disclosed in U.S. Pat. No. 6,077,236 issued to Cunningham. Implantable leads incorporating accelerometer-based cardiac wall motion sensors are generally disclosed in U.S. Pat. No. 5,628,777 issued to Moberg, et al. A device for sensing natural heart acceleration is generally disclosed in U.S. Pat. No. 5,693,075, issued to Plicchi, et al. A system for myocardial tensiometery including a tensiometric element disposed at a location subject to bending due to cardiac contractions is generally disclosed in U.S. Pat. No. 5,261,418 issued to Ferek-Petric et al. All of the above-cited patents are hereby incorporated herein by reference in their entirety.
It is apparent from the above discussion that a need remains for providing a device and method for monitoring the mechanical effects of delivering one or more electrical pulses to the heart to ensure that a patient is in fact receiving a desired therapy.